The mammalian octapeptide FLQPQRFamide (F8Fa, neuropeptide FF, NPFF) an "anti-opioid" peptide, plays a role in opiate dependence and subsequent abstinence syndrome. An antagonist of this peptide may, therefore, alleviate opioid tolerance and dependence, and allow for the management of opiate abstinence syndrome. The peptide antagonist used as a lead compound does not reach the central nervous system (CNS) after systemic administration, because it is lipid-insoluble and unable to penetrate the blood-brain barrier. The objective is to develop such antagonists that can be administered parenterally (by i.v. injection, subcutaneously, etc.), and transport the pharmacologically active agents into the CNS (chemical delivery systems, CDSs). A neuropeptide FF antagonist daYFLQPQRa (daY8Ra, an N-terminal desaminotyrosine-blocked peptide amide containing the 1-7 residues of F8Fa) was used as a lead compound to design CDSs that renders the peptide lipid-soluble in order to enhance access to the CNS by passive transport, and allow enzymatic conversions within the CNS at the attached functional groups to prevent the peptide from leaving the CNS after delivery. Finally, the active antagonist is released by sequential metabolism. Analogs of daY8Ra will also be designed by a) removing the FLFQ segment from day8ra, b) by replacing the N-terminal desaminotyrosine (daY) of daY8Ra with an N-alkylated nicotinamide residue to eliminate the need for an activating step, and c) by combining a and b. The compounds will be synthesized by solid and solution-phase syntheses based on the sequential elongation of the peptide chain, then coupling appropriate peptide segments that possess the desired targeting and protecting functional groups. In vitro stability/metabolism studies will be used to confirm the occurrence of the designed metabolic changes and to investigate metabolic changes and to investigate metabolic properties crucial to the sequential bioactivation involved in CNS-targeting CNS- uptake and retention of the CDSs after i.v. injection of the CDSs to rats will be evaluated by measuring the concentration of the antagonist and its precursor(s) in brain tissue as a function of time. Pharmacological evaluation of the brain-targeted NPFF antagonists will include the quasi- morphine abstinence syndrome (QMAS) induced by i.c.v. NPFF in rats, and CNS-targeting of pharmacologically significant amount of NPFF antagonist by the CDS approach will be assessed by using the abstinence syndrome participated by naloxone in morphine-dependent rats as a paradigm. Teeth chattering/chewing, writhes/grasps, shakes and tremors, and ptosis as measures of the QMAS and naloxone-participated abstinence will be recorded for groups of animals, and the effect of the compounds will be statistically evaluated. Based on the attenuation of abstinence syndromes, metabolic stability data, and CNS-distribution studies, candidates will be selected for further structure-based design, biochemical, pharmaceutical and pharmacological studies that continue preclinical development of these potential new drugs.